Hydrology PDF

 INTRODUCTION TO HYDROLOGY HYDROLOGY Evaporation is the process through Hydrology is the study of water science. which an element or compound changes Examines the distribution, occurrence, from a liquid to a gaseous state below the and circulation of water o...

 INTRODUCTION TO HYDROLOGY HYDROLOGY Evaporation is the process through Hydrology is the study of water science. which an element or compound changes Examines the distribution, occurrence, from a liquid to a gaseous state below the and circulation of water on Earth and in boiling point; in the context of the water the Earth's atmosphere. cycle, this process is specifically how liquid It deals with water found in lakes and water enters the atmosphere as water vapor. streams, precipitation and snowfall, snow The humidity of the air is restored by and ice on the ground, and water found in evaporation. It plays a significant role in the the pores of rocks and soil. energy exchange that generates atmospheric An interdisciplinary field that draws on motion, which in turn determines weather a variety of related sciences, including and climate in the Earth-atmosphere meteorology, geology, statistics, chemistry, system. physics, and fluid mechanics. Temperature, relative humidity, wind speed, and solar radiation are the primary factors influencing evaporation. Ninety percent of the water in the atmosphere comes from evaporation, with the other 10% coming from the release of water vapor by plant leaves. Water is continuously circulated TRANSPIRATION throughout the Earth-atmosphere system as part of the hydrologic cycle. The movement of water from the ground to the atmosphere and back again is the The process by which water leaves plant fundamental component of the water through their stomata is called transpiration. cycle. On the underside of leaves, stomata are EVAPORATION tiny holes that connect to the vascular tissues of plants. For the majority of plants, transpiration is a passive process that is mostly regulated by soil moisture content and atmospheric humidity.  Just 1% of the water that transpires PRECIPITATION through a plant is utilized by the plant to grow. 99 percent of it is released into the atmosphere. Evapotranspiration is the combined Any liquid or frozen water that condense components of evaporation and in the atmosphere and returns to the earth is transpiration, and is sometimes used to called precipitation. It can take on various evaluate the movement of water in the forms, such as snow, sleet, and rain. atmosphere. Even in cases where the water came from CONDENSATION the ocean, precipitation is always fresh water. This is because water does not cause sea salt to evaporate. Water droplets can, however, occasionally become contaminated by The process that turns water vapor into airborne pollutants before they hit the a liquid state is called condensation. ground. Condensation in the atmosphere can Acid rain is the term for the precipitation manifest as dew or clouds. that arises from this. Although acid rain does This is also the mechanism by which not directly harm people, it can increase the water accumulates on the exterior of a can acidity of lakes and streams. Because plants or bottle of non-insulated cold beverage. and animals frequently cannot adapt to the The air temperature and the dewpoint acidity, this damages aquatic ecosystems temperature are the two temperatures that determine condensation, not a single RUNOFF temperature. The temperature at which Runoff refers to precipitation that dew can form is known as the "dew point," reached areas where water collects from which also happens to be the point at the ground surface without being absorbed which air gets saturated and loses its ability into the soil or evaporating. In addition to to hold water vapor. Water vapor condenses causing erosion, runoff transports materials with any further cooling. from the ground's surface to the rivers where the water ends up. Additionally, it may pollute water.  Merely 35 percent of precipitation finds its way into the ocean or sea. The soil absorbs the remaining 65%. A portion of it also evaporates. INFILTRATION PERCOLATION Infiltration and percolation are two related but different processes describing the movement of water through soil. Infiltration is defined as thedownward entry of water MAJOR COMPONENTS into the soil or rock surface and percolation is the flow of water through soil and porous or fractured rock. STORAGE The planet's atmosphere contains water that can be transported across its surface rather quickly. The geologic characteristics of the These terms should not be used soil and rock types found at the storage sites synonymously with permeability. have a significant impact on the types of Permeability is the property or capacity storage that take place both above and below of a porous rock, sediment, or soil for ground. Oceans, lakes, reservoirs, and transmitting a fluid. Essentially, glaciers are examples of surface storage; soil, permeability is how well water can flow aquifers, and the fissures in rock formations through a material, while percolation and are examples of underground storage. infiltration are the rates at which water can travel through materials  WATER BUDGET EQUATION The continuity equation for water in its different phases for a given area, let's say a In the planetary water cycle, there are catchment, over a period of time is three main places where water is stored. expressed as Water is kept in three different places: 𝑴𝒂𝒔𝒔 𝒊𝒏𝒇𝒍𝒐𝒘 − 𝒎𝒂𝒔𝒔 𝒐𝒖𝒕𝒇𝒍𝒐𝒘 = 𝒄𝒉𝒂𝒏𝒈𝒆𝒔 the earth’s surface, the atmosphere, and 𝒊𝒏 𝒎𝒂𝒔𝒔 𝒔𝒕𝒐𝒓𝒂𝒈𝒆 the ground. If the mass storage volumes, outflow volume, and inflow volume have the same WATER BUDGET density One hydrological tool for measuring the 𝑽𝐢− 𝑽𝐨 = ∆𝑺 amount of water entering and leaving a Rainfall– runoff relation system is a water budget. To put it another 𝑹=𝑷−𝑳 way, it is a list of all the water that is exchanged and stored in the atmosphere Water Budget Equation (precipitation, evaporation), subsurface 𝑷 − 𝑹 − 𝑮 − 𝑬 − 𝑻 = ∆𝑺 (aquifer, groundwater), and land surface Wherein: (rivers, lakes). P– precipitation The idea behind a water budget is that the R– surface runoff amount and rate at which water enters and G– net groundwater flow out of the exits a region balances the rate of change catchment of water stored in that region. E– evaporation Hydrological engineers use this idea as the T– transpiration cornerstone for efficient management, ∆𝑆– change in storage planning, and sustainability of water resources. Storage 𝑺 = 𝑺𝒔 + 𝑺𝒔𝒎 + 𝑺𝒈 𝐼𝑛𝑓𝑙𝑜𝑤 = 𝑂𝑢𝑡𝑓𝑙𝑜𝑤 ± 𝐶ℎ𝑎𝑛𝑔𝑒𝑠 𝑖𝑛 𝑆𝑡𝑜𝑟𝑎𝑔𝑒 Wherein: 𝑆𝑠– surface water storage 𝑆𝑠𝑚– water in storage as soil moisture 𝑆𝑔– water in storage as groundwater  Residence Time Table 2 – Global Annual Water Balance Average duration of stay of a particle of water in a reservoir 𝑻𝒓 =𝑽/𝑸 Wherein: 𝑽– volume of water 𝑸– average flowrate WATER BALANCE APPLICATION IN ENGINEERING It is estimated that there are 1386 million cubic kilometers of water in the world. The oceans hold 96.5% of this water in the form of saline water. A portion of the water on land, or roughly 1% of the total water, is saline as well. As a result, there is only roughly 35.0 million 𝑘𝑚3 of fresh water accessible. The remaining 24.4 million 𝑘𝑚3 The design and administration of water are frozen as ice in the polar regions, on resources engineering projects heavily top of mountains, and on glaciers. Of this, depend on hydrology, which has an impact about 10.6 million cubic kilometers are on a number of crucial areas including both liquid and fresh. irrigation systems, municipal water supply, flood control systems, hydroelectric power Table 1 – Estimated World Water Quantities generation, and navigation infrastructure. Engineers and planners can maximize the sustainability and efficiency of these projects by using hydrological principles. This ensures that water resources are managed effectively to meet present and future needs while minimizing potential risks and environmental impacts. SAMPLE PROBLEM A LAKE HAD A WATER SURFACE ELEVATION OF 103.200m ABOVE DATUM AT THE BEGINNING OF A CERTAIN MONTH. IN THAT MONTH THE LAKE RECEIVED AN AVERAGE INFLOW OF 6.0m3/s FROM SURFACE RUNOFF SOURCES. IN THE SAME PERIOD, THE OUTFLOW FROM THE LAKE HAD AN AVERAGE VALUE OF 6.5m3/s. FURTHER, IN THAT MONTH, THE LAKE RECEIVED RAINFALL OF 145mm AND THE EVAPORATION 1 FROM THE LAKE SURFACE WAS ESTIMATED AS 6.10cm. WRITE THE WATER BUDGET EQUATION FOR THE LAKE SURFACE AREA CAN BE TAKEN AS 5000 ha. ASSUME THAT THERE IS NO CONTRIBUTION TO OR FROM THE GROUNDWATER STORAGE. USE 30 DAYS PER MONTH. 1. DETERMINE THE CHANGE IN THE VOLUME OF THE STORAGE. 2. DETERMINE THE NEW WATER ELEVATION. SOLUTION: ELEV = 103 20 m. ① AS = ? In flow 6 m3s In +10w(l) Gm 130 days) (24hrs) (cominSee = = Outflow = 6. 5 m3 (in) Rainfall = 145 mm = 15 55x10. m3 Evaporation = 6 10 Cm. Area 5000 ha Inflow (2) 145mm)mmm)(5000ha) (10000m a = = , use 30 days/month = 7. 25x106 In flow = ( 15 55 + 7 25).. (109) = 22 8X109. " outflow (1) = 6 5. 3 (30) (24) (60) (60) = 16. 85x10 (2) G outflow = (5000(10000) = 3. 05X10 Outflow = 16 85 x 103 + 3 05 X106.. = 19. 9 x106 AS = In flow-outflow = 22 8 X. 100 - 19 9. X 106 = 2. 9 X 106 m3 volume = Axh volume = U A rea 2. 9 X106 = 0 058. 5000(10000 New Elev = 103 2 + 0.. 058 = 103 258M. SAMPLE PROBLEM A SMALL CATCHMENT OF AREA 150ha RECEIVED A RAINFALL OF 10.5cm IN 90mins DUE TO A STORM. AT THE OUTLET OF THE CATCHMENT, THE STREAM DRAINING THE CATCHMENT WAS DRY BEFORE THE STORM AND EXPERIENCED A RUNOFF LASTING FOR 10 hours WITH AN AVERAGE DISCHARGE OF 1.5m3/s. THE STREAM WAS AGAIN DRY AFTER THE RUNOFF EVENT. 1. WHAT IS THE AMOUNT OF WATER WHICH WAS NOT AVAILABLE TO RUNOFF DUE TO COMBINED EFFECT OF INFILTRATION, EVAPORATION AND TRANSPIRATION? 2. WHAT IS THE RATIO OF RUNOFF TO PRECIPITATION? 3. BY ASSUMING THAT ALL THE SURFACE RUNOFF TO THE OCEANS COMES FROM THE RIVERS, FIND THE RESIDENCE TIME OF GLOBAL RIVERS IN DAYS. USE THE TABLE OF ESTIMATED WORLD WATER QUANTITIES AND GLOBAL ANNUAL WATER BALANCE. PROVIDE YOUR ANSWER IN NEAREST WHOLE NUMBER. SOLUTION: A = 150 ha Rainfall - Runoff Relation Rainfall = 10 5 cm. ; 90 mins. R= P L - Runoff = 1 5. m315 ; 10 hours 5 m3 (10 hours) /60mins) (bea Runoff = 1. = 54 , 000 m3 Rainfall = 10 5 (150 na) (10, 000). 100 = 157 , 500 m Runoff = Precipitation - losses  losses = Precipitation - Run off = 157, 500 - 54 000 , = 103 , 500 m3 Run off Ratio = Precipitation 54 , 000 = 157 , 500 = 0. 34 v 0. 00212 X103km3 T = I Q 0 0474 44 700 , Is =. yn = 0. 0474(360) = 17 07. days = 18 days